Materials Engineering Exam - Fall 2007, Exams of Materials science

Download Materials Engineering Exam - Fall 2007 and more Exams Materials science in PDF only on Docsity! Mat E 443 Exam 2 – Fall 2007 Problem Possible Score 1 15 2 15 3 15 4 10 5 15 6 15 Total 85 INSTRUCTIONS – Read Carefully: 1. This exam is to be worked by each student, individually. Show all work, attaching additional sheets if necessary. Please write neatly so that proper credit can be given. 2. Students may freely refer to: - any printed references, articles, or textbooks - any Web materials posted for this course - the student’s own notes from lecture. 3. Once the exam period begins, students may NOT refer to: - any other person (student, faculty, or other) - any website other than the MatE443 WebCT site - any notes or exams written by other current or previous MatE443 students. 4. Read the exam carefully. Submit any questions to the instructor via email. Questions and answers will be made viewable to all students. 4. The exam period begins at 6pm (noon), 5-Nov-2007. 5. The exam is to be turned in at the start of class (11:00am) Wednesday, 7-Nov-2007. Name: ____________________________ 1. For each set of steels in (a) and (b) below, rank the hardenability. (1= highest hardenability, 2- next highest, etc.) (a) Measured critical diameters for different steels in different quench media: (5 pts) Steel H dC (mm) Rank A 0.1 6 B 0.25 15 C 0.5 18 D 1.0 25 E 5.0 31 (b) The following steel compositions: (5 pts) Steel ASTM Grain Size Rank 1080 6 1340 8 4130 5 4340 4 8620 7 (c) Use the Jominy curves below to estimate the critical diameters for 4130 steel in water and oil quenchants. Determine the corresponding ideal diameter and compare with your result for 4130 in part (b). (5 pts) 4. The solid circles below represent a plane of iron atoms in austenite. What are the Miller indices of this plane? (2 pts) The dashed circle represents an iron atom in an adjacent plane above the solid circles. The shaded circle represents a carbon atom in the interstitial site just above the three associated iron atoms. Is the carbon atom in an octahedral or a tetrahedral site? (2 pts) In terms of interstitial sites in the relevant structures, explain the role of interstitial carbon in the martensite transition and the corresponding change in crystal structure (i.e. c/a ratio). (50 words max.) (6 pts) 5. The sketch below shows the Fe atom positions on a particular crystal plane in a martensitic structure. Before the ’ transition, this plane was the {111} plane. What martensite crystal plane is depicted? (2 pts) ( ___ ___ ___ ) (Please assign specific plane indices.) On the figure, clearly draw and label three arrows to show: - any direction of the 111 type (2 pts) - any direction of the 110 type (2 pts) - any direction of the 100 type (2 pts) * Please label the specific direction for each, using hkl rather than hkl . Estimate the composition of this plain carbon steel (i.e. carbon content). (4 pts) Give the characteristics you would expect in this martensite. (3 pts) - habit plane: _______________________ - morphology type: _______________________ - dominant deformation mechanism: _______________________ 6. For each numbered description, enter the letter identifying the appropriate term from the list below. a. Martensite start b. Lath Martensite c. Plate Martensite d. Ferrite e. Cementite f. Pearlite g. Bainite h. Hardness i. Hardenability j. Jominy Test k. Charpy Test l. H-Test m. Grossman Test n. Grossman number o. Kurdjumov-Sachs relation p. Nishiyama-Wasserman relation q. Martempering r. Austempering s. Autotempering t. Tempering u. Blue brittleness v. Tempered martensite embrittlement w. Secondary hardening x. Maraging y. Retained austenite z. Subcritical Anneal aa. Spheroidizing anneal bb. Normalizing cc. Full Anneal dd. Critical diameter ee. Ideal critical diameter ff. Widmanstatten structure gg. Acicular ferrite 1. A heat treatment consisting of a quench to an intermediate temperature followed by an isothermal hold, intended to result in bainite formation. 2. The ratio between the convective heat transfer coefficient to the thermal diffusivity of the steel, indicating the effectiveness as a quenchant. 3. A standardized test designed to characterize the hardenability of a steel. 4. A process that results in severe degradation in toughness due to the decomposition of retained austenite, with cementite forming a continuous film, typically along prior austenite boundaries. 5. A loss in ductility associated with the segregation of elements such as phosphorus and sulfur to austenite grain boundaries prior to quenching. 6. A heat treatment that involves (i) quenching to a temperature above MS, (ii) holding until the temperature becomes uniform throughout the part, (iii) quenching and tempering. 7. A heat treatment designed to improve the toughness of a quenched steel. 8. A process that may occur in a steel with a high MS, where the martensite that forms just below MS may begin to decompose during the quenching process. 9. A process where alloy steels may achieve very high strength from the precipitation of alloy carbides during a high temperature tempering treatment. 10. A process where intermetallics precipitate during a subcritical heat treatment, giving rise to very high strength steels. 11. The low-carbon variety of the metastable body-centered tetragonal phase, typically forming on {111} habit planes. 12. The high-carbon variety of the metastable body-centered tetragonal phase, typically forming on {225} habit planes. 13. A two-phase lamellar microconstituent, comprised of ferrite and cementite, which forms through a coupled growth mechanism. 14. A two-phase microconstituent, comprised of ferrite and carbide, which forms through precipitation of supersaturated ferrite accompanied by microsegregation of carbon and precipitation of fine carbides. 15. The maximum diameter round bar that can be through-hardened by quenching in a given quenchant.